The communication of information is a necessity of modern society, which is enabled through the operation of a communication system. Information is communicated between a sending station and a receiving station by way of a communication channel. The sending station converts the information into a form for communication over the communication channel. The receiving station detects and recovers the information for the benefit of a user. A wide variety of different types of communication systems have been developed and are regularly employed to effectuate communication between sending and receiving stations.
An exemplary communication system is a cellular communication system in which a communication channel is defined upon a radio link extending between sending and receiving stations. Cellular radio communication systems are amenable to implementation as mobile communication systems wherein radio links, rather than fixed, wireline connections, are employed to define communication channels.
Generally, a cellular communication system includes a network infrastructure that includes a plurality of base stations that are positioned at spaced-apart locations throughout a geographic area. Each of the base stations defines an area, referred to as a cell, from which the cellular communication system derives its name. The network infrastructure, of which the base stations form portions thereof, is coupled to a core network such as a packet data backbone or a public-switched telephone network. Communication devices such as computer servers, telephone stations, etc., are, in turn, coupled to the core network and are capable of communication by way of the network infrastructure and the core network. Portable transceivers, commonly referred to as user equipment or mobile stations, communicate with the base stations by way of such radio links.
As wireless communication systems such as cellular telephone, satellite, and microwave communication systems become widely deployed and continue to attract a growing number of users, there is a pressing need to accommodate a large and variable number of communication systems transmitting the growing volume of data with a fixed resource, such as a fixed channel bandwidth, to accommodate a fixed data packet size. Traditional communication system designs employing a fixed resource (e.g., a fixed data rate for each mobile station) have become challenged to provide high, but flexible, data transmission rates in view of the rapidly growing customer base.
As a user equipment is moved through the physical area served by a wireless communication system (e.g., as a user equipment is transported in a moving vehicle), it is frequently necessary to reassign communication resources with their limited availability for the user equipment from a source base station to a target base station that provides better signal coverage for the new location. The user equipment has already been assigned uplink resources on the packet uplink shared channel (“UL-SCH”) to perform the necessary communication functions with the source base station by a packet scheduler in the source base station. To continue communication with the target base station, new uplink resources are assigned by the target base station for use by the user equipment.
In system arrangements of the past, initiation of the uplink transmission by a target base station is performed by a user equipment using a contention-based access arrangement on an uplink random access channel (“RACH”), which is (statically) reserved for the particular purpose of user equipment transmitting the access bursts. Access bursts are initially transmitted to the target base station by the user equipment to allow the target base station to measure uplink communication parameters such as transmission delay, signal amplitude, and other parameters that may be needed by the target base station to establish a reliable uplink for the user equipment. Transmission of access bursts from different user equipment is inherently unsynchronized in such communication systems. Accordingly, one or more user equipment during handover, or even when initiating a new communication with a base station, may transmit access bursts that arrive simultaneously at a target base station with access bursts of another user equipment, thereby causing a signal collision event.
The use of a contention-based handover procedure based on a random access channel presents an unresolved issue in the currently envisioned Third Generation Partnership Project (“3GPP”) evolved universal mobile telecommunications system terrestrial radio access network (“e-UTRAN”). Disadvantages of contention-based handover include, among other system performance issues, possible handover delay between base stations, handover interrupt time or gap, and the overall questions regarding reliability and repeatability of the handover process. Contention-based handover may also introduce limitations on the scheduling of RACH resources in the communication system. Planning of the RACH may also become more complex when contention-based handover is employed. Thus, a non-contention based handover would advantageously provide a number of benefits over a contention-based handover.
Considering the limitations of a contention-based handover as described above, a system and method to assign communication resources to user equipment for operation in the serving area of a target base station to execute a non-contention-based handover to a target base station is not presently available, thereby incurring many of the aforementioned limitations. In accordance therewith, a non-contention-based handover system and method in a communication system employing a plurality of base stations would provide improved resource utilization and communication efficiency.